The main rotor blades of an UAV-helicopter (UAV, Unmanned Aerial Vehicle) are subjected to loads during operation, e.g. pulsating bending forces which are transmitted from the rotor blades to the vertical rotor mast. The rotor mast is provided with a hub to which the rotor blades are mounted with the aid of rotor blade holders. One way of reducing the loads acting on the rotor blades is to make the hub tiltable so that the hub is allowed to deflect with respect to the rotor mast when subjected to said loads. As a result, the loads acting on the rotor blades can be reduced.
Such main rotor arrangements are disclosed in U.S. Pat. No. 4,092,084 and U.S. Pat. No. 5,544,844. The disclosed solutions are provided with end stops so that the maximum deflection can be restricted, but they are not capable of controlling the deflection in any other way.